A number sign (#) is used with this entry because of evidence that Poirier-Bienvenu neurodevelopmental syndrome (POBINDS) is caused by heterozygous mutation in the CSNK2B gene (115441) on chromosome 6p21.

Poirier-Bienvenu neurodevelopmental syndrome (POBINDS) is a neurologic disorder characterized in most cases by early-onset seizures and variably impaired intellectual development (ID). The severity of neurologic impairment is highly variable: some patients may have refractory seizures and be bedridden with no meaningful speech, whereas others may have treatment-responsive seizures and achieve normal psychomotor development (summary by Li et al., 2019).

Poirier et al. (2017) reported 2 unrelated male patients, aged 10 and 19 years, with POBINDS. Both had mild early developmental delay with delayed walking and walking difficulties, as well as learning difficulties with significant speech delay. One patient had attention deficit and autistic features, but no seizures. The other patient developed refractory myoclonic epilepsy at 18 months of age; EEG showed generalized spike/wave discharges and slowed background activity. Both patients were noted to have variable dysmorphic features around adolescence, including prognathism, open mouth with protruding tongue, bushy eyebrows, flat philtrum, dental anomalies, strabismus, and downturned corners of the mouth. Brain imaging was normal in the patient without seizures, but showed white matter hyperintensities in the patient with seizures.

Sakaguchi et al. (2017) reported a 21-month-old Japanese boy with POBINDS. He presented in early infancy with mild developmental delay and daily myoclonus. At age 10 months, he developed complex partial seizures. EEG was consistent with cortical origin of the myoclonus; brain imaging was normal. He was able to speak a few words and walk by himself, but had impaired intellectual development.

Nakashima et al. (2019) reported 2 unrelated children of Malaysian (patient 3) and Japanese (patient 4) origin with a severe form of POBINDS. Both presented in the first 2 months of life with refractory seizures, including focal, focal evolving to generalized tonic-clonic, and evolution to epileptic encephalopathy in 1 patient. At 15 and 7 years of age, both patients had profoundly impaired global development: they were bedridden with no speech and had not achieved sitting. Brain imaging showed cerebellar atrophy in 1 patient and mega cisterna magna in the other.

Li et al. (2019) reported 9 unrelated Chinese children, ranging in age from 6 months to 6 years, with POBINDS. All had onset of generalized tonic-clonic seizures before 12 months of age, including 8 with onset before 6 months of age. One patient also had myoclonus. EEG was normal in 5 patients, and brain imaging was normal in 7, whereas 2 patients showed nonspecific poor myelination and enlarged subarachnoid space, respectively, on imaging. Four patients became seizure-free after monotherapy, and 3 became seizure-free with polytherapy. The most severely affected patient (patient 1) was a 6-year-old boy with profoundly impaired ID, inability to walk, and absent language. He had refractory myoclonic and generalized epilepsy with multiple spikes on EEG. By contrast, 4 patients had mildly impaired ID, 1 had moderate ID, and 3 of the 7 patients who became seizure-free had normal intelligence and acquired normal developmental milestones. The findings suggested that impaired intellectual development is a common finding in this disorder, even if seizures are well-controlled.

The heterozygous mutations in the CSNK2B gene that were identified in patients with POBINDS by Poirier et al. (2017) and Nakashima et al. (2019) occurred de novo.

In 2 unrelated patients with POBINDS, Poirier et al. (2017) identified de novo heterozygous splice site mutations in the CSNK2B gene (115441.0001 and 115441.0002). The mutations, which were found by trio-based whole-exome sequencing and confirmed by Sanger sequencing, were not found in the 1000 Genomes Project or ExAC databases. Analysis of patient cells showed decreased mRNA levels compared to controls, and RT-PCR showed that the mutations resulted in exon skipping and premature termination, consistent with haploinsufficiency and a loss of function. However, the authors noted that the mutations may induce the production of an aberrant truncated protein. Poirier et al. (2017) postulated that the mutations may cause abnormal dopamine signaling.

In a 21-month-old Japanese boy with POBINDS, Sakaguchi et al. (2017) identified a de novo heterozygous frameshift mutation in the CSNK2B gene (115441.0003). The mutation was found by trio-based whole-exome sequencing and confirmed by Sanger sequencing. Functional studies of the variant and studies of patient cells were not performed, but the variant was predicted to result in haploinsufficiency.

In a 15-year-old Malaysian girl (patient 3) with POBINDS, Nakashima et al. (2019) identified a de novo heterozygous frameshift mutation in the CSNK2B gene (115441.0004). The mutation, which was found by trio-based whole-exome sequencing and confirmed by Sanger sequencing, was classified as pathogenic according to ACMG guidelines. Transfection of the mutation into HEK293 cells showed that the mutant protein was expressed, but was unable to bind with CSNK2A1 (115440), which may induce instability of the CK2 holoenzyme. A missense variant (H165R) at a highly conserved residue was identified in another unrelated patient (patient 4) with a similar disorder, but limited functional studies did not indicate a pathogenic effect, and the variant was classified as 'likely pathogenic' according to ACMG guidelines.

In 9 unrelated patients with POBINDS, Li et al. (2019) identified de novo heterozygous mutations in the CSNK2B gene (see, e.g., 115441.0005-115441.0007). The mutations, which were found by trio-based whole-exome sequencing of a cohort of 816 probands with epilepsy, were confirmed by Sanger sequencing. The mutations occurred throughout the gene and comprised 4 missense variants, 3 frameshifts, and 1 splice site mutation. None of the variants were found in the 1000 Genomes Project or gnomAD databases; all were predicted to be pathogenic (8) or likely pathogenic (1) by ACMG criteria, but only 4 had predictive evidence of 'very strong' pathogenicity. Functional studies of the variants and studies of patient cells were not performed. Five variants occurred in the zinc-binding domain, suggesting a hotspot; patients with these variants responded to antiepileptic treatment. However, patients with missense mutations could have a severe phenotype and those with frameshift mutations could have a mild phenotype, precluding establishment of a definitive genotype/phenotype correlation.